Furuno FS-1570, Service Manual

Page: 141 / 322

5.4 TX/RX Board (05P0733)
5-24
Oscillation frequency
First, second and third local oscillators generate F+72.455 MHz, 72 MHz and 455 kHz
respectively. The 1st local oscillator consists of PLL and DDS circuits. The PLL circuit
uses the output of the DDS circuit as a reference signal. The local oscillator frequency
varies according to emission modes as shown in Table 5.4.1.
Table 5.4.1 Oscillation frequency of local oscillator
MODE 1st Lo 2nd Lo 3rd Lo
USB F+72.455 MHz+1.5 kHz 456.5 kHz
LSB F+72.455 MHz
–
1.5 kHz 453.5 kHz
Tx 456.5 kHz
H3E
Rx
—
TLX 456.7 kHz
FAX
F+72.455 MHz
72 MHz
456.9 kHz
The PLL circuit includes four oscillation coils, T11, T12, T13 and T14 for 30 MHz
frequency range. These coils are selected depending on frequency setting. Each
oscillation circuit is used in lower and upper bands.
Table 5.4.2 PLL oscillation frequency
BAND Oscillation coil Setting frequency VCO frequency
1-L 0.1 to 2.99999MHz 72.55500 to 75.45499MHz
1-H
T11
3.0 to 5.99999MHz 75.45500 to 78.45499MHz
2-L 6.0 to 9.49999MHz 78.45500 to 81.94599MHz
2-H
T12
9.5 to 13.49999MHz 81.95500 to 85.95499MHz
3-L 13.5 to 17.49999MHz 85.95500 to 89.95499MHz
3-H
T13
17.5 to 21.49999MHz 89.95500 to 93.95499MHz
4-L 21.5 to 25.49999MHz 93.95500 to 97.95499MHz
4-H
T14
25.5 to 29.99999MHz 97.95500 to 102.45499MHz
Offset frequency: 0 kHz(Mode:H3E, TLX, FAX)
SSB(USB) mode: add 1.5 kHz